Offset selector



Sept 5, 1967 .1. P. HUFFMAN ETAT. 3,340,502

OFFSET SELECTOR 2 Sheets-Sheet 1 AFiled June l5, 1964 555mm Ewhr v .O.. OZDOmPDO l .TVO

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mznomz. l? T; o 295mm I NVENTORS .RHUFFMAN AND BY J.H AUER JR. K

THEIR ATTORNEY 'All' ZOCOmm N .OE

QZDOmFDO Sept 5. 1957 J. P. HUFFMAN ETAL 3,340,592

OFFSET SELECTR Filed June l5, 1964 2 Shee'LS-Shee*I United States Patent C) 3,340,502 OFFSET SELECTOR Jerry P. Huffman, Rochester, and .lohn H. Auer, Jr.,

Fairport, N.Y., assignors to General Signal Corporation, Rochester, N.Y., a corporation of New York Filed .lune 15, 1964, Ser. No. 374,945 7 Claims. (Cl. 340-35) This invention relates to traic control systems, and more particularly to an improved system for selecting offsets for traffic signals along a section of highway in accordance with demands of traffic.

Offset may be defined as the number of seconds or percent of the time cycle at which a green indication appears at a given trafhc control signal after a predetermined instant constituting a time reference. For smooth traiiic progression along an urban arterial highway, successive traffic signals encountered by arterial traffic should be green. This requires that the offset for each successive trafiic signal be greater than the offset for the preceding traffic signal. For proper control of traffic signals, a plurality of offsets should be provided for each signal. One particular offset for each signal may then `be selected by energization of a single lead connected from a central control point to each traffic signal controller.

To -avoid congestion and facilitate arterial traffic fiow, it is necessary to control offsets in accordance with demand on the highways. Since traffic varies with time, weather conditions, etc., the most efficient way to achieve such control is to select offsets automatically, in accordance with trafhc demand on the highway. Moreover, interconnection of traffic signals along arterial highway is necessary in order to promote smooth trafiic fiow, since efficient control of signals along a section of highway requires that all traffic conditions within that section `be taken into account along with significant conditions within both adjacent sections.

A typical prior art offset selector is shown in I. H. Auer, Ir., et al. application Ser. No. 354,886, filed March 26, 1964, now Patent No. 3,307,146, issued Feb. 28, 1967, This earlier version required both AC and DC power supplies for its oper-ation. The present invention represents an improvement over the aforementioned application that only DC power is required for operation. This eliminates all requirements for phase detection circuits and. their associated transformers.

The invention as herein proposed permits individual control of trafiic signal offsets .at each traffic signal local controller along a section of artery, from a single offset selector. This is accomplished by dividing the artery into a number of arterial sections, each section encompassing a plurality of local controllers and a single offset selector. Each offset selector supplies offset signals to the local controllers in the arterial section associated therewith, based upon actual traffic conditions within the section and specified significant conditions within adjacent sections. Conditions within the adjacent sections are sensed through interconnections between the offset selector for each arterial section and the offset selectors for each adjacent section. Hence, offset changes can be produced progressively along the artery in accordance with traffic conditions, enabling traffic to fiow through the artery with a minimum of delay.

Two traffic control parameters which may be used in combination to accurately refiect traffic conditions along a highway are lane occupancy and volume. Lane occupancy may be defined as the percentage of highway which is vehicle-occupied at any given instant of time; however, since this is a spatial concept, continuous measurement of which is rather dithcult, lane occupancy is more frequently expressed as a percentage ratio of vehicle presence time to total time at any specified detection point. This ratio is a close approximation of spatial lane occupancy, provided traffic is moving along at a relatively constant speed, which is generally the case under moderateto-heavy traffic conditions. Besides being an accurate measurement of tramo conditions, the parameter to traffic lane occupancy may readily be computed with a minimum of equipment and circuit complexity.

Traihc volume may be expressed as the number of vehicles passing `a particular point during any given period of time. This parameter is a fairly accurate measure of trafiic congestion, provided traffic is free-fiowing; however, as congestion increases, and speed of traffic is restricted accordingly, traffic volume no longer represents an accurate measure of traffic congestion since the rate of vehicles passing a point during a given interval of time is substantially decreased, indicating low congestion. when, in actuality congestion is at a very high level.

The invention contemplates utilization of both lane occupancy and volume parameters, in order to provide highly accurate selection of offsets in accordance with -actual traffic conditions. This is accomplished by selecting the greater of vthese parameters as that upon which to base the offset selection. In this fashion, the parameter most accurately depicting traffic conditions is that upon which the offset selection is based. Under relatively light trafiic conditions, this parameter is usually volume, while under relatively heavy traffic conditions, this parameter is usually lane occupancy.

The offset selector comprises first and second switching means, each providing an output voltage of amplitude substantially equal to the maximum voltage amplitude supplied to the inputs. The first switching means is responsive to the greater one of inbound lane occupancy and volume parameters within a specified section of arterial highway, and the second switching means is responsive to the greater one of outbound lane occupancy and volume parameters Within the specified section. Outputs of the first and second switching means are coupled to a third switching means which provides an output voltage substantially equal to the greater one of the output voltages supplied by the first and second switching means. In addition, the outputs of the first `and second switching means are supplied to a subtracting means, which provides an output manifestation of the difference in output voltage amplitudes produced by the first and second switching means. The third switching means and the subtracting means are interconnected by a circuit means having a plurality of outputs, whereby preselected ones of the plurality of outputs are energized in accordance with the output conditions of the third switching means and the subtracting means.

Accordingly, selection means trollers along of traffic.

Another object is to provide a direct current system for selecting offsets for traffic controllers along a highway in accordance with either volume or lane occupancy conditions, whichever is greater, in both inbound ,and outbound directions.

Another object is to provide -a direct current system for selecting offsets for traffic signal controllers located along a section of a vehicular route based upon demands of existing trafiic within the section and existing trafiic within both adjacent sections.

Another object is to provide a traffic control system for one object of this invention is to provide for producing offset signals for traffic cona highway in `accordance with demands a sectionalized artery wherein tradic signal controllers for each section are independently controlled from separate odset selection means, each selection means being dependent upon volume and lane occupancy conditions within the section controlled therefrom and volume and lane occupancy conditions within both adjacent sections.

The foregoing and other objects and advantages of the invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of a system embodying the invention.

FIG. 2 is a block diagram of an odset computer, such as utilized in the system of FIG. 1.

FIG. 3 is a part schematic and part block diagram of the offset selector for section B of the artery of FIG. 1.

FIG. 4 is a chart illustrating odset coding as produced by the odset selector.

Turning to FIG. l, there is shown a portion of a tradie artery 1 divided into three sections. A separate odset computer is associated with each section. Hence, a section A odset computer is associated with arterial section A, a section B odset computer is associated with arterial section B and a section C odset computer is associated with arterial section C.

Each section has .a number of intersections with secondary streets. A tratlic signal is located at each of these intersections, and each signal is controlled by an individual local controller. For example, in section B, tradic signals SBI, SBZ and SB3 are controlled respectively by local controllers LB1, LB2 and LB3. The local controllers in each section receive a signal from the odset computer associated therewith. For example, controllers LB1, LB2 and -LB3 receive odset signals from the section B odset computer.

Suitable vehicle detectors, such as presence detectors of the type disclosed in H. C. Kendall, 1. H. Auer, I r., N. A. Bolton and K. H. Frielinghaus Patent 3,042,303 issued July 3, 1962, are situated within each section, preferably at a point just inside the intersections formed by the secondary streets crossing each section at either end of the section. At each of these intersections, detection of both inbound and outbound tradic is performed. Thus, in each section, two detections are made of both inbound and outbound tradic. For example, in section B, detectors B11 and B12 are used for detecting traic in the inbound direction, while detectors B01 and B02 are used for detecting traffic in the outbound direction. Although a single intersection is shown in each section between the detectors for the section, a plurality of intersections with the section may exist between the detectors at either end. Moreover, although for simplicity of explanation the artery is assumed to have but a single inbound and single outbound lane, for a multi-lane artery tradlc conditions in each lane could be detected separately.

1n a fashion similar to that described for section B, detectors A11 and A12 detect inbound traic in section A at either end, while detectors A01 and AO?. detect outbound tradic in section A at either end. Similarly, detectors C11 and C12 detect inbound tradic in section C at either end,

Y while detectors CO1 and CO2 detect outbound tradic in section C at either end. Detectors A11, A12, A01 and A02 provide information to the section A odset computer, while detectors C11, C12, CO1 and CO2 provide information to the section C odset computer.

Y Each section odset computer provides information for the adjacent section computer on either side, which pertains to existing traiiic conditions within the'center section. For example, information relating' to inbound trai-lic in section B and outbound trac in section B is supplied from the section B odset computer to the section A odset computer and section C odset computer, respectively. 1n similar fashion, information relating to inbound traiic in section C is supplied from the section C odset computer to the section B odset computer, while information relating to outbound tradc in section A is supplied from the section A odset computer to the section B odset computer. This information is in the form of either a lane occupancy or volume signal, in every case.

Thus, in the fashion shown generally in FIG. 1, odset control of traffic signals along a lengthy artery may be achieved. The system is virtually unlimited by the number of sections into which the artery may be divided. Moreover, each section may contain a large number of local controllers, in accordance with a large number of secondary cross streets intersecting the section.

FIG. 2 is a block diagram of a typical section odset computer. For exemplary purposes, the odset computer shown is assumed to be that used with section B. The computer is seen to comprise an inbound lane occupancy computer 2, an inbound volume computer 3, an outbound lane occupancy computer 4 and an outbound Volume computer 5. The inbound and outbound lane -occupancy computers may be of the type disclosed in I. H. Auer, Jr., et al. U.S. Patent No. 3,278,896, issued Oct. 1l, 1966, while the inbound and outbound volume computers may comprise any of the types which are well known in the art.

Input voltages are supplied to inbound lane occupancy computer 2 and inbound volume computer 3, in parallel, from detectors B11 and B12. Similarly, input voltages are supplied to outbound lane Voccupancy computer 4 and outbound Volume computer 5, in parallel, from detectors B01 and B02. Output voltages produced by the inbound lane occupancy and volume computers are each supplied to separate inputs of an odset selector 6, the circuitry of which is described infra. Similarly, output voltages produced by the outbound lane occupancy and volume computers are each supplied to separate inputs of odset selector 6. The means for accomplishing selection of odsets by the odset selector is described infra.

A third input voltage, constituting an inbound influence, is supplied to odset selector 6 from the odset selector of the section C odset computer, while a fourth input voltage, constituting an outbound influence, is supplied to odset selector 6 from the odset selector of the section A odset computer. In similar fashion, one output voltage from the section B odset computer, constituting an inbound influence, is furnished to the odset selector of section A, while another output voltage from the section B odset computer, constituting an outbound influence, is supplied to the odset selector of the section C odset computer. A preselected odset voltage produced by odset selector 6 is furnished simultaneously to local controllers LB1, LB2 and LB3 of section B.

Briefly described, operation of the section B odset computer is as follows. The inbound lane occupancy and volume computers supply inbound traic parameter voltages to odset selector 6, while the outbound lane occupancy and volume computers supply outbound traflic parameter voltages to odset selector 6. The odset selector weighs the inbound and outbound voltages, and makes` a determination as to the level of the greatest tradic congestion, independently of direction. A second determination is made by the odset selector by subtracting the lcomposite outbound signal, which includes the outbound lnuence signal from section A, from the composite inbound signal, which includes the inbound induence signal from section C, and one of a plurality of outputs is then energized in accordance with both of tthe aforementioned determinations. This energized output thus represents a selected odset signal for the local controllers of section B.

Turning now to the odset selector circuit of FIG.-3, there is shown a plurality of -diodes 10, 11, 12 and 13, the anodes of which are coupled respectively to potentiometers 14, 15, 16 and 17. Positive potential is supplied to potentiometer 14 from lane occupancy computer 2 of FIG. 2, which is responsive to traffic in the inbound direction Within section B of the highway of FIG. 1, while positive potential is supplied to potentiometer 15 from volume computer 3 of FIG. 2, which is responsiveV to trac in the inbound direction within this section of highway. Similarly, positive potential is supplied to potentiometer 16 from lane occupancy computer 4 of FIG. 2, which is responsive to traffic in the outbound direction within section B of the highway, while positive potential is supplied to potentiometer 17 from volume computer 5 of FIG. 2, which is responsive to traffic in the outbound direction within this section of highway. The cathodes of diodes and 11 are both coupled through a diode 18 to the input of a level monitor having five output levels and designated absolute level monitor 20. Similarly, the cathodes of diodes 12 and 13 are both coupled to the input of absolute level monitor 20 through a diode 19. Level monitor 20 has associated therewith a group of four front and back contacts 21, 22, 23 and 24, for producing the five output levels. Negative bias is supplied to the heel of contact 21, while front contact 21 is coupled to the heel of contact 22, front contact 22 is coupled to the heel of contact 23 and front contact 23 is coupled to the heel of contact 24.

The cathodes of diodes 12 and 13 are both connected to provide a positive input voltage to a summing amplifier 25. Similarly, the cathodes of diodes 19 and 11 provide a positive input voltage to an inverter amplifier 26, the output of which provides a negative input voltage to summing amplifier 25. In addition, the cathodes of diodes 12 and 13 provide positive energy constituting an outbound influence to the offset computer for section C. Similarly, the negative output voltage of inverter amplifier 26 is supplied to the offset computer for section A to provide an inbound influence. In similar fashion, a positive voltage comprising an outbound influence from the offset computer of section A is supplied through a potentiometer 27 to an input of summing amplifier 25, while a negative voltage representing an inbound influence from the offset computer of section C is supplied through a potentiometer 28 to an input of summing amplifier 25. The purpose of the potentiometer used in this circuit is to attenuate the amplitude of input voltages to desired levels and thereby control the extent to which each individual input voltage affects the overall circuit operation.

Output voltage from summing amplifier is supplied to the input of an inverter amplifier 30 and to the anode of a diode 31. Output voltage produced by inverter amplifier 30 is supplied to the anode of a ydiode 32. The cathodes of diodes 31 and 32 are jointly connected to the input of a difference level monitor 33 which drives a first pair of contacts 34 and 35 in unison and a second pair of contacts 36 and 37 in unison. The heel of contact 34 is coupled to back contact 22 of absolute level monitor 20, While the heel of contact 35 is coupled to back contact 23 of absolute level monitor 20. The heel of contact 36 is coupled to front contact 35 of difference level monitor 33, While the heel of contact 37 is coupled to front contact 24 of absolute level monitor 20. It is noted that level monitors 20 and 33 may, for example, assume the level monitor configuration disclosed in the aforementioned I. H. Auer, Jr., et al. application Ser. No. 354,886.

Output voltage from summing amplifier 25 is also supplied to a polarity detector circuit 4f). This circuit comprises a first transistor 41 having its collector connected to ground through a load resistor 42 and its emitter connected to a source of negative potential. Output voltage produced by summing amplifier 25 is resistively coupled to the base of transistor 41. A second transistor 43 receives base potential from the collector of transistor 41. The emitter of transistor 43 is biased slightly less negative than the emitter of transistor 41 by the voltage drop across a diode 44. This permits the base of transistor 43 to be driven sufficiently negative with respect to the emitter to render the transistor non-conductive. A relay 45 having a plurality of contacts 46, 47 and 48 is connected in series with the collector of transistor 43. A diode 49 is shunted across the relay in order to protect transistor 43 against high voltage transients produced when relay 45 is deenergized.

The heel of contact 46 is coupled to front contact 37 of difference level monito-r 33. Similarly, the heel of contact 47 is coupled to front contact 36 of difference level monitor 33, while the heel of contact 4S is coupled to both back contact 36 and front contact 34 of difference level monitor 33. In this fashion, a plurality of offsets may be produced by the circuit of FIG. 3. More particularly, energization of front contact 46 provides a forced outbound offset FO, while energization of Iback contact 46 provides a forced inbound offset FI. These offsets are utilized under extremely heavy trafc conditions in either the outbound or inbound directions, respectively, and constitute operation of the traffic signals in a reverse progression, enabling the lead vehicles in a line of trafc to move on, prior to admitting following vehicles to the segment of highway vacated by the lead vehicles.

Back contact 24 of absolute level monitor 20 is connected to back contact 37 of difference level monitor 33, whereby energization of either of these two back contacts produces a simultaneous offset signal S. This signal operates all traffic signal controllers in unison; that is, all signals are green simultaneously on a common single phase, yellow simultaneously on that phase, and red simultaneously on that phase. This offset may be used when traffic conditions are extremely heavy in both the inbound and outbound directions, simultaneously.

Energization of front contact 47 of relay 45 provides an out-bound offset signal O, while energization of back Contact 47 provides an inbound offset signal I. The outbound and inbound offset signals are produced under lmoderate traffic conditions. Similarly, energization of -front contact 48 of relay 40 provides a pre-outbound offset signal PO, while energization of back contact 48 provides a pre-inbound offset signal PI. The pre-outbound and pre-inbound signals indicate that traffic levels are generally below those requiring a simultaneous offset or an outbound or inbound offset. Energization of either back `contact 34 or 35 of different level monitor 33 produces a balanced offset signal BAL, which indicates that traffic con-gestion conditions are substantially equal in both dilrections and are greater than conditions designated light, but less than conditions requiring a simultaneous offset signal. Energization of back contact 21 of absolute level monitor 20 provides a light oset signal L, indicative of very light traffic conditions in both directions.

In operation, the amplitude of positive voltage supplied to the input of absolute level monitor 20 corresponds to the largest of the input signals supplied to the system from the inbound and outbound lane occupancy and volume computers after the weighting effect of potentiometers 14, 15, 16 and 17. This is due to the action of each pair of diodes 10 and 11, 12 and 13, and 1S and 19. Each of these pairs comprises a voltage amplitude selector switch. A positive voltage supplied to the anode of Ione of the diodes in any of the aforementioned selector switches which exceeds the amplitude of positive voltage supplied to the anode of the other diode in that switch, appears at the cathode of the one diode to comprise the output voltage of the switch, while back-biasing the other diode of the switch to tender it non-conductive. In this manner, only the voltage of greatest amplitude supplied to each selector switch appears at the output of the switch. Moreover, this voltage may represent either lane occupancy or volume, depending upon the relative amplitudes of these parameters and the settings of potentiometers 14-17. Thus, absolute level monitor 20 responds solely to the greatest amount of traffic congestion, Whether it be in the inbound or outbound direction, and whether it be measured in terms of lane occupancy or volume. Moreover, as the amplitude of voltage supplied to absolute level monitor 20 is increased, the level monitor closes its front contacts 21, 22, 23 and 24, in that order, thereby providing five steps into which the grestest level of traic congestion may be classified. These steps designated 1L-5L from the lowest level to the highest level, are indicated in the left margin of the chart of FIG. 4.

Positive voltages representing the greater of either weighted lane occupancy or volume in the outbound direction, along with an outbound influence parameter from section A, and negative voltages representing the greater of either weighted lane occupancy or volume in the inbound direction, along with an inbound infiuence parameter from section C, are supplied to summing amplifier 25. Therefore, the output voltage of summing amplifier 25 may assume either a positive or negative polarity,l depending upon whether the total of outbound or inbound voltage amplitudes supplied thereto is greatest. It is noted that an inversion takes place in summing amplifier 25. Therefore, a negative output voltage produced Vby the summing amplifier indicates that traffic congestion in the outbound direction exceeds traffic congestion in the inbound direction, while a positive output voltage produced by the summing amplifier indicates that trafiic congestion in the inbound direction exceeds traffic congestion in the outbound direction.

Output voltage produced by summing amplifier 25 is supplied to difference level monitor 33 through diode 31, provided inbound traffic congestion exceeds outbound traffic congestion. When outbound traffic congestion exceeds inbound traffic congestion, the voltage produced by summing amplifier 25 -is supplied to difference level monitor 33 through inverter 30 in series with diode 32. Therefore, it is obvious that difference level monitor 33 responds to the magnitude of difference between traffic congestion levels in the inbound and outbound direction.

' When this difference is extremely slight, or at a NIL level, level monitor 33 maintains all its back contacts closed. As this difference increases to a level designated AA, front contacts 34 and 35 are closed. As this difference increases further to another level designated BB, front contacts 36 and 37 of level monitor 33 are also closed. These levels are indicated in the lower margin of the chart in FIG. 4, for both negative and positive levels as sensed by polarity detector 40. Hence, when inbound traic congestion exceeds outbound traffic congestion, a positive voltage is produced at the output of summing amplifier 25, which when applied to the base of transistor 41 drives the transistor into conduction. This produ-ces a voltage drop across resistor 42, which drives the base of transistor 43 negative. Transistor 43 is thereby switched into its non-conductive mode, causing relay 45 to deenergize. This represents the condition when inbound traffic congestion exceeds outbound traffic congestion, and is designated I-. On the other hand, When outbound traffic congestion exceeds inbound trafiic congestion, output voltage produced by summing amplifier 25 is negative. This drives transistor 41 out of conduction, thereby raising the base voltage on transistor 43, switching transistor 43 into its conductive mode. Relay 45 is thus energized, indicating that outbound trafiic congestion exceeds inbound trafiic congestion. This condition denotes existence of a negative difference in traffic level, and is designated Reference to the chart of FIG. 4 indicates that existence of a positive difference level of AA or BB indicates inbound traffic congestion exceeds outbound traffic congestion, existence of a negative difference level of AA or BB indicates that outbound traffic congestion exceeds inbound traffic congestion, and existence of level NIL indicates outbound and inbound traffic congestion are approximately equal. This, in turn, determines whether either an inbound or outbound offset is to be supplied. This determination is also combined with the determination of the maximum absolute level of traffic, whether it be in the inbound or outbound direction, and an offset is selected in accordance with both of these determinations, as set forth in the chart of FIG. 4.

Thus, there has been shown a novel system for selecting one of a plurality of offsets for traffic signals along a section of artery, depending upon the greatest weighted level of either lane occupancy or volume in the inbound or outbound direc-tions, along with the level of difference between congestion in the inbound and outbound directions and existing traiiic Vconditions within both adjacent sections. The circuitry involved is simple, easy to maintain, and requires .only direct current for operation. The system further provides capability for producing forced inbound, forced outbound and simultaneous offsets in the event trafiic congestion rises to extremely high levels.

Although but one embodiment of the invention has been described, it is to be specifically understood that this form is selected to facilitate in disclosure of the invention rather than to limit the number of forms which it may assume; various modifications and adaptations may be applied to the specific fonm shown to meet requirements of practice, without in any manner departing from the spirit or scope of the invention.

What is claimed is:

1. Trafiic signal offset selector apparatus for supplying predetermined offset `controls to a plurality of traffic signal controllers in a predetermined section of highway in response -to traffic congestion conditions comprising first means responsive to traffic moving in said predetermined section in an inbound direction and generating a first signal representative of inbound trafiic congestion in said section, second means responsive to traic moving in said predetermined section in an outbound direction and generating a second signal representative of outbound traffic congestion in said section, third means coupled to said first and second means for providing a third signal representative of the magnitude of the greater of said first and second signals, subtracting means coupled to said first and second means and providing a fourth signal representative of the difference in amplitudes of said first and second signals, and control means responsive to said third and fourth signals for selecting a predetermined offset for Y spectively representative of a corresponding one of said 1 first and second signals, and means coupled to said subtracting means and providing an output manifestation in response to the polarity of said fourth signal, said control means being responsive also to said output manifestation. l

3. The offset selector of claim 2 wherein said control means includes first level, monitoring means coupled to said third means and operated in response tothe amplitude of signal produced by said third means, and second level monitoring means coupled to said subtracting means and operated in response to the amplitude of voltage produced by said subtracting means.

4. The apparatus of claim 1 in which said first andY second signals are respectively responsive to inbound and outbound traic volume in said predetermined section of highway.

5. The apparatus of claim 1 in which said first and second signals are respectively responsive to inbound and outbound lane occupancy in said predetermined section of highway.

6. The apparatus of claim 1 in which said first means includes means for generating signals representative respectively of both traffic volume and lane occupancy in said predetermined section and further includes means for controlling said first signal to be responsive at all times to the greater of said volume and lane occupancy signals, said second means also including means for generating both outbound volume and lane occupancy signals and including also further means for controlling said second signals to be representative of the greater of said two signals.

7. The apparatus of claim 1 in which said apparatus also includes means responsive to traic in sections of highway adjacent to the respective ends of said predetermined section, and moving in a direction toward said section, said control means being also responsive to said last-named means.

References Cited UNITED STATES PATENTS 2,542,978 2/ 1951 Barker 340-35 2,932,003 4/ 1960 Barker 340-38 3,241,107 3/1966 Vivier 340-35 NEIL C. READ, Primary Examiner. THOMAS B. HABECKER, Examiner. 

1. TRAFFIC SIGNAL OFFSET SELECTOR APPARATUS FOR SUPPLYING PREDETERMINED OFFSET CONTROLS TO A PLURALITY OF TRAFFIC SIGNAL CONTROLLERS IN A PREDETERMINED SECTION OF HIGHWAY SIGNAL CONTROLLERS IN A PREDETERMINED SECTION OF HIGHWAY FIRST MEANS RESPONSIVE TO TRAFFIC MOVING IN SAID PREDETERMINED SECTION IN AN INBOUND DIRECTION AND GENERATING A FIRST SIGNAL REPRESENTATIVE OF INBOUND TRAFFIC CONGESTION IN SAID SECTION, SECOND MEANS RESPONSIVE TO TRAFFIC MOVING IN SAID PREDETERMINED SECTION IN AN OUTBOUND DIRECTION AND GENERATING A SECOND SIGNAL REPRESENTATIVE OF OUTBOUND TRAFFIC CONGESTION IN SAID SECTION, THIRD MEANS COUPLED TO SAID FIRST AND SECOND MEANS FOR PROVIDING A THIRD SIGNAL RESPRESENTATIVE OF THE MAGNITUDE OF THE GREATER OF SAID FIRST AND SECOND SIGNALS, SUBTRACTING MEANS COUPLED TO SAID FIRST AND SECOND MEANS AND PROVIDING A FOURTH SIGNAL REPRESENTATIVE OF THE DIFFERENCE IN AMPLITUDES OF SAID FIRST AND SAID PLURALITY OF TRAFFIC SIGNAL CONTROLLERS. 